Effectn of Wave Form on Dissipated Energy During Fatigue of Wood.

从木材破坏的时间依赖性出发，研究了木材的破坏机理，发现木材的疲劳破坏机理与静态破坏机理相似，但破坏过程不同。疲劳失效不仅与时间因素有关，还与载荷重复次数有关，重复加载过程中所消耗的能量为疲劳失效提供了重要信息。在疲劳过程中所测得的耗散能包括两部分，一部分是由木材流变特性的内摩擦引起的耗散能，另一部分是由导致试件失效的微观损伤引起的耗散能。疲劳极限应力可由分步重复试验获得的耗散能估算。也就是说，疲劳极限是在耗散能开始超过根据耗散能和阶跃应力之间的线性关系计算出的量时的应力。另一方面，疲劳失效时间可以从与损伤相关的耗散能量和阶跃应力之间的经验关系（指数函数）来估计。进一步理解经验函数的物理意义有助于解释疲劳破坏的机理，试样的损伤与时间和重复因子有关。这就需要一个包含时间和重复因素相互干扰的非线性损伤理论，才能清楚地揭示疲劳破坏的机理。

Failure mechanism of wood was investigated from the time dependency of wood failure.This research revealed that the mechanism of fatigue failure was similar to that of static failure but the process differs. The fatigue failure deals with not only time factor but also the factor of load repetition number.The dissipated energy generated during the repetitive loading provides important information on the fatigue failure. Amount of the dissipated energy which is measured during the fatigue process consists of two parts, the part caused by internal friction of rheological property of wood and another part is that by microscopical damage which induces the failure of a testing specimen. The fatigue limit stress can be estimated by the dissipated energy obtained by the stepwise repeat test. Namely the fatigue limit is given as the stress at the point where the dissipated energy begins to surpass the amount which is calculated from the linear relation between the dissipated energy and the stepwise stress. On the other hand the fatigue failure time can be estimated from an empirical relation ( an exponential function) between the dissipated energy related to the damage and the stepwise stress. More over understanding physical meaning of the empirical function will help to explain the mechanism of fatigue failure.The time- and the repetition factor dependently cause damages to the specimen. It needs a non-linear damage theory consisting of a mutual interference of time and repetition factors, to clearly show the mechanism fatigue failure.